346 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Ill discussing the question of South Carolina oyster food in its many aspects, the 
general character should first he examined. The oyster, it is well known, is quite an 
epicure in its feeding, preying almost entirely upon the minute, lowly organized plants 
that float or swim in its neighborhood. With shell slightly opened, and with the dark- 
colored sensory margins of its mantle protruding, it draws into its shell a narrowing, 
food -bearing water current. At once it draws in the current, carefully screens out the 
minute food particles, and passes out a stream of filtered water. It avoids, if possible, 
ingesting sand or mud. 
The food organisms are readily taken for examination from the oyster’s stomach. 
The tip of the soft body of the oyster is removed by a single clip of the scissors, and 
a pointed pipette is introduced at once into the stomach cavity, and the fluid contents, 
rich golden-brown in color, are drawn up. The stomach contents of a number of oys- 
ters from the same locality may be taken and put in labeled homeopathic vials, from 
which a number of dippings of both sediment and fluid should at ouce be examined. 
Oyster food, it will be found, consists mainly of diatoms, a particular kind of 
minute, lowly organized plant, that have the remarkable power of moving freely about 
in the water. Unlike any other plants, they are incased in a pair of saucer-like glassy 
shells, fitted one to the other like the lid to a pill box. These delicate shells are the 
natural prey of every microscopist. He admires their varied shapes (round, S-like, 
elliptical, or three-cornered) and tests his lenses upon the delicate pits, ridges, and 
traceries shown in their glassy structure. A photomicrograph (Plate lxvii, Fig. 1) 
shows the delicate basket-work markings of a cleaned shell of a Surirella gemma, a 
diatom not uncommon in Carolina oyster stomachs. The glassy cases of the minute 
plants appear in no way to inconvenience the oyster’s digestion. The mucilaginous 
sheathing that encases prominently many diatoms is first dissolved, and the digestive 
juices find their way through the intricate glassy valves, speedily attacking and reducing 
the jelly-like contents, together with the inclosed golden-brown pigment pellets. The 
emptied diatoms appear to settle gradually, and are soon brushed by countless cilia 
from the stomach to the intestine. 
The food organisms of the Chesapeake oyster are given by Prof. Ryder in the 
report of the Maryland Fish Commission for 1881, p. 20. The food of the Long Island 
oyster is discussed by the writer in the report of the New York Oyster Investigation, 
1886. In the latter paper was noted the extreme importance of the plant element of 
oyster food, examination showing that about 90 per cent of the ingested organisms 
were diatoms. The animals ingested were few in number, and sometimes unwelcome. 
In South Carolina the elements of the oyster food are practically those of Long- 
Island. The proportion of its component organisms may thus be generally stated: 
1. Animal life — ( a ) Crustaceans, ( b ) worms, (c) protozoans 
2. Vegetable — (a) Diatoms 90 
(6) Fragments and reproductive bodies of seaweeds 2 
( c ) Pine pollen 3 
